Stainless Steel Coil Tube (Coiltube) — Intermittent Evaporator Series

Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed primarily for use in intermittent evaporator systems and related heat exchange applications, this coil tube is formed by cold-bending high-grade austenitic stainless steel seamless tubes into a continuous spiral or helical configuration. The resulting product combines the corrosion resistance and hygienic properties of stainless steel with the high surface-area-to-volume ratio inherent in coiled geometry, making it an optimal solution for thermal transfer in batch-processing environments.

Coil tubes are integral components in a wide range of industrial and commercial systems, including refrigeration condensers, evaporators, heat exchangers, water heating systems, and process engineering equipment. The intermittent evaporator application—central to this product line—requires coil tubes that can withstand repeated thermal cycling, resist scaling and fouling, and maintain structural integrity under cyclic pressure differentials.

Material & Properties

The coil tubes are fabricated from austenitic stainless steel grades conforming to international standards. The primary material specifications are as follows:

• Material Grades: SUS 304 (UNS S30408), SUS 304L (UNS S30403), SUS 316 (UNS S31608), SUS 316L (UNS S31603), SUS 321 (UNS S32108), SUS 310S (UNS S31008)
• Equivalent Standards: AISI 304/304L/316/316L/321/310S, EN 1.4301/1.4307/1.4401/1.4404/1.4845/1.4845, GB/T 12771, GB/T 13296
• Chemical Composition (Typical — SUS 316L):
  • Carbon (C): ≤ 0.030%
  • Chromium (Cr): 16.0% – 18.0%
  • Nickel (Ni): 10.0% – 14.0%
  • Molybdenum (Mo): 2.0% – 3.0%
  • Iron (Fe): Balance
• Mechanical Properties (Cold-Worked Condition):
  • Tensile Strength (UTS): ≥ 520 MPa (75,400 psi)
  • Yield Strength (0.2% Proof): ≥ 205 MPa (29,700 psi)
  • Elongation: ≥ 40%
  • Hardness: ≤ 250 HV (Hardness Vickers)
• Physical Properties:
  • Density: 7.98 g/cm³
  • Thermal Conductivity (at 20°C): 16.3 W/(m·K)
  • Thermal Conductivity (at 100°C): 19.9 W/(m·K)
  • Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
  • Specific Heat (20–100°C): 502 J/(kg·K)
  • Melting Point: 1375 – 1400°C
• Corrosion Resistance: Excellent resistance to atmospheric corrosion, acidic and alkaline environments, chlorinated solutions (particularly 316/316L grades), and most organic compounds. The passive chromium oxide layer (Cr₂O₃) provides self-healing protection against oxidation.
• Hygienic Properties: Non-toxic, non-flavor-imparting, and resistant to microbial growth (biofilm formation), making the product suitable for food-grade, pharmaceutical, and potable water applications.

Specifications

Parameter	Specification Range	Unit	Applicable Standard
Outer Diameter (OD)	Φ3.0 – Φ50.8	mm	ASTM A213 / GB/T 12771
Wall Thickness (WT)	0.3 – 3.0	mm	ASTM A213 / GB/T 12771
Coil Diameter (CD)	Φ100 – Φ2000	mm	Custom / Project-Specific
Coil Length (CL)	1 – 500	m	Custom / Project-Specific
Number of Turns	5 – 5000	turns	Custom / Project-Specific
Tolerance on OD	±0.05 mm (fine tolerance) / ±0.1 mm (standard)	mm	ASTM A213
Tolerance on WT	±0.03 mm (fine tolerance) / ±0.05 mm (standard)	mm	ASTM A213
Surface Finish	BA (Bright Annealed) / Pickled & Polished / Mirror (Ra ≤ 0.4 μm)	—	ASTM A269 / GB/T 12771
End Treatment	Plain Cut / Beveled / Threaded / Flanged / Socket Weld	—	ASME B31.3 / GB/T 12771
Coil Pitch	1.5× OD – 3.0× OD (adjustable)	—	Project-Specific
Operating Temperature	-196°C to +870°C (continuous)	°C	ASME BPV Code
Maximum Working Pressure	Up to 10.0	MPa	ASME B31.3
Welding Compatibility	TIG (GTAW), MIG (GMAW), Resistance Welding, Orbital Welding	—	ASME Section IX
Testing Methods	Hydrostatic Test, Helium Leak Test, Eddy Current Testing, Spectroscopic Analysis	—	ASTM A213 / EN 10217

Manufacturing Process

The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous, multi-stage manufacturing protocol designed to ensure dimensional accuracy, mechanical integrity, and surface quality:

1. Raw Material Selection & Inspection: High-purity stainless steel seamless tubes are sourced from certified mills and subjected to incoming quality control including spectroscopic chemical analysis (OES/PMS), mechanical property verification, and visual surface inspection.
2. Tube Straightening & Cutting: Seamless tubes are straightened using hydraulic or mechanical straightening equipment and cut to the required blank length with precision saws or laser cutting systems to ensure clean, burr-free ends.
3. Surface Preparation: Tubes undergo pickling and passivation treatment to remove mill scale, oxidation, and surface contaminants, establishing a uniform passive oxide layer critical for corrosion resistance.
4. Cold Coiling (Helical Forming): The straightened tube is fed through a precision-controlled coiling head equipped with multi-axis rollers. The coiling process is performed at ambient temperature (cold forming) to preserve the metallurgical properties of the austenitic stainless steel. The coil diameter, pitch, and number of turns are precisely controlled by CNC-operated equipment to meet exact project specifications.
5. Post-Forming Stress Relief (if required): For applications demanding minimal residual stress, the coiled tube may undergo solution annealing (1050°C – 1150°C) followed by controlled cooling to relieve cold-work-induced residual stresses and restore full ductility.
6. End Processing: Tube ends are processed according to the specified connection type—beveling (per ASME B31.3), threading, flanging, or socket welding preparation—ensuring compatibility with downstream assembly requirements.
7. Quality Testing & Inspection: Each coil tube undergoes comprehensive testing including:
   • Hydrostatic pressure testing (at 1.5× maximum working pressure, per ASTM A213)
   • Dimensional verification (OD, WT, coil diameter, pitch using CMM or laser measurement systems)
   • Surface finish measurement (Ra values via profilometry)
   • Eddy current testing for internal and external surface defect detection
   • Helium leak detection for critical pressure-retaining applications
8. Packaging & Traceability: Finished coil tubes are individually identified with unique batch/heat numbers, packaged in protective wrapping (wooden crates, foam-lined containers, or shrink-wrapped reels), and shipped with full mill test certificates (MTC) and quality documentation.

Applications

The stainless steel coil tube is engineered for a diverse range of industrial, commercial, and specialized applications. Key application areas include:

• Intermittent Evaporator Systems: The primary application domain. Coil tubes serve as the heat exchange surface in batch evaporators used for concentrating liquids (e.g., sugar solutions, chemical concentrates, pharmaceutical extracts) where thermal cycling and intermittent operation are characteristic.
• Refrigeration & HVAC (Heating, Ventilation & Air Conditioning): Condenser and evaporator coils for chillers, heat pumps, and air conditioning units, leveraging the high heat transfer efficiency of coiled geometry.
• Food & Beverage Processing: Milk pasteurization, juice concentration, and brewing systems where sanitary-grade stainless steel (304/316L) is mandated by FDA and EHEDG standards.
• Pharmaceutical Manufacturing: CIP (Clean-in-Place) compatible heat exchange coils for sterilization, distillation, and process heating in GMP-regulated environments.
• Chemical Processing: Reactor cooling coils, distillation column internals, and heat exchangers handling corrosive media (acids, chlorides, caustic solutions).
• Power Generation: Condenser tubes in power plant steam cycles and waste heat recovery systems.
• Marine & Offshore Engineering: Seawater-cooled heat exchangers and condensers where 316L stainless steel provides superior resistance to chloride-induced pitting and crevice corrosion.
• Automotive & Aerospace: Lightweight heat exchange coils for vehicle radiators, aftercoolers, and aerospace thermal management systems.
• Oil & Gas: Subsea heat exchangers, gas dehydration coils, and process piping in upstream and midstream facilities.

Quality Certifications & Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and product certification portfolio ensuring full compliance with international standards:

• ISO 9001:2015 — Quality Management System certification, demonstrating consistent ability to provide products and services that meet customer and regulatory requirements.
• ISO 14001:2015 — Environmental Management System certification, reflecting commitment to sustainable manufacturing practices and environmental stewardship.
• ISO 45001:2018 — Occupational Health and Safety Management System certification.
• ASME "S" / "U" Stamp — Authorization for manufacturing pressure-containing components in compliance with ASME Boiler and Pressure Vessel Code.
• EN 10204 3.1 / 3.2 Test Certificates — Material test certificates issued by authorized inspection bodies, providing traceability from raw material to finished product.
• CE Marking — Conformity with European directives including Pressure Equipment Directive (PED 2014/68/EU) for applicable products.
• GB/T Standards Compliance — Full compliance with Chinese national standards for stainless steel tubes (GB/T 12771, GB/T 13296, GB/T 21832).
• Material Traceability — Each production batch is traceable to the original mill heat number, with complete documentation of chemical composition, mechanical properties, and all manufacturing process parameters.
• Third-Party Inspection — Products available for independent inspection by recognized bodies (e.g., SGS, Bureau Veritas, TÜV, DNV) upon customer request.

Unique Selling Points

1. Precision Coiling Technology: CNC-controlled coiling equipment ensures repeatable coil geometry with minimal dimensional variation, critical for consistent heat transfer performance in evaporator applications.

2. Full Material Grade Portfolio: Availability of multiple stainless steel grades (304, 304L, 316, 316L, 321, 310S) enables precise material selection matched to specific chemical environments and operating conditions.

3. Custom Engineering Capability: Flexible manufacturing parameters (OD, WT, coil diameter, pitch, length, end treatment) allow tailoring to exact project specifications, supporting both standard and bespoke coil configurations.

4. Intermittent Evaporator Optimization: The coil tube design is specifically validated for intermittent thermal cycling, with demonstrated fatigue resistance and dimensional stability under repeated heating and cooling cycles—a critical requirement for batch processing applications.

5. Comprehensive Quality Assurance: End-to-end quality control from incoming material inspection through final hydrostatic and leak testing, backed by full traceability documentation and internationally recognized certifications.

6. Surface Finish Excellence: Availability of BA, polished, and mirror-finish surfaces (Ra ≤ 0.4 μm) meeting hygienic and sanitary requirements for food-grade, pharmaceutical, and potable water applications.

Technical Notes

When selecting coil tube specifications for intermittent evaporator applications, the following engineering considerations are recommended:

• Material grade selection should account for the chemical composition of the process fluid, particularly chloride content (favoring 316L for chloride-rich environments) and operating temperature (favoring 321 or 310S for sustained temperatures above 600°C to prevent intergranular corrosion).
• Coil pitch should be optimized to balance heat transfer efficiency against fluid flow resistance; a pitch of 2.0× OD is generally recommended as a starting point for evaporator coil design.
• Wall thickness selection must satisfy both pressure design requirements (per ASME B31.3 or equivalent) and minimum thickness criteria for mechanical stability of the coiled geometry.
• For applications involving thermal cycling, post-coiling stress relief annealing is recommended to minimize the risk of stress-corrosion cracking (SC